Dynamic properties of wind turbines such as resonance frequencies and damping coefficients are dependent on the wind turbines operating conditions such as wind speed, foundation properties, soil properties and other conditions.
Fatigue of wind turbine parts and, therefore, lifetime of the wind turbine may depend on such dynamic properties.
It may be important for the owner of a wind turbine to be able to determine changes in the expected lifetime of a wind turbine due to changes in dynamic properties, e.g. in order to calculate the expected profit of the wind turbine investment.
Accordingly, there is a need for determining dynamic properties and changes in dynamic properties of wind turbines.
EP2103915A1 discloses an apparatus for determining a resonant frequency of a wind turbine tower, comprising a processing unit configured to receive an acceleration measurement value, said acceleration measurement value being representative of the acceleration of the wind turbine tower in the direction parallel to a rotor rotational axis of the wind turbine and/or in the direction perpendicular to both the rotor rotational axis and the tower axis of the wind turbine. The processing unit comprises a Fourier transform module configured to calculate a spectral vector and a resonant frequency calculation module configured to calculate the tower resonant frequency based on the calculated spectral vector.
The inventors of the present invention have appreciated that improved method for determining dynamic properties of wind turbines would be of benefit, and have in consequence devised the present invention.